Respiration-synchronized heart sound trending

ABSTRACT

Respiration-synchronized heart sound trends can be detected using an implantable medical device, including a respiration sensor, a respiration phase detector, a heart sound sensor, a heart sound detector, and a processor. The implantable medical device can also include a cardiac sensor. The respiration-synchronized heart sound trends can include heart sounds occurring during specific phases of a respiration signal, such as inspiration or expiration. The heart sound signal can be gated or the heart sound sensor can be enabled or disabled using the cardiac sensor or the respiration sensor. Further, the heart sound trends can be displayed using an external display, and can provide information about a cardiovascular status using an analysis module, or the analysis module and a blood volume sensor.

TECHNICAL FIELD

This patent document pertains generally to cardiac health, and more particularly, but not by way of limitation, to respiration-synchronized heart sound trending.

BACKGROUND

The heart is the center of the circulatory system of the human body. The left-sided chambers of the heart, including the left atrium and the left ventricle, draw oxygenated blood from the lungs and pump it to the organs of the body to provide the organs with oxygen. The right-sided chambers of the heart, including the right atrium and the right ventricle, draw deoxygenated blood from the organs and pump it into the lungs where the blood gets oxygenated.

The lungs are the center of the respiratory system of the human body. Respiration generally includes inhalation and exhalation. Inhalation is the act of bringing air into the lungs. As the diaphragm contracts, the airspace volume of the thorax increases, resulting in a decreased intrathoracic pressure. The decreased intrathoracic pressure draws air into the lungs. As the diaphragm relaxes, the airspace volume of the thorax decreases. The resulting increased intrathoracic pressure forces excess air out of the lungs.

Aerobic respiration, the process of energy production in the human body, typically requires oxygen as fuel and produces carbon dioxide as a by-product. The respiratory system generally draws oxygen into the body and expels carbon-dioxide into the atmosphere. During inhalation, oxygen-rich air is brought into the lungs, where the oxygen is diffused into the blood. During exhalation, carbon dioxide is released from the blood into the atmosphere.

Typically, as the human body requires more oxygen for energy production, cardiac activity increases. Thus, because cardiac performance typically varies depending on the state of respiration, a relationship exists between the cardiovascular and respiratory systems of the body.

OVERVIEW

This summary is intended to provide an overview of the subject matter of the present patent application. It is not intended to provide an exclusive or exhaustive explanation of the invention. The detailed description is included to provide further information about the subject matter of the present patent application.

In Example 1, a system includes an implantable medical device. The implantable medical device includes a respiration sensor, configured to sense a respiration signal. The implantable medical device also includes a heart sound sensor, configured to sense a heart sound signal. The system also includes an implantable or external respiration phase detector, coupled to the respiration sensor, configured to detect at least one phase of the respiration signal. The system also includes an implantable or external heart sound detector, coupled to the heart sound sensor, configured to detect at least one heart sound of the heart sound signal. The system also includes an implantable or external processor, coupled to the respiration phase detector and the heart sound detector, wherein the processor is configured to automatically produce at least one heart sound trend over at least a portion of at least one respiration cycle using the at least one heart sound, the at least one heart sound trend occurring during a specified at least a portion of at least one phase of the respiration signal.

In Example 2, the at least one heart sound trend of Example 1 optionally includes at least one measurement, feature, characteristic, computation, or interval of at least one heart sound.

In Example 3, the at least one measurement, feature, characteristic, computation, or interval of at least one heart sound of Examples 1-2 optionally includes at least one of an amplitude of a heart sound, a time interval between a first heart sound and a second heart sound, and a normalized amplitude or interval of at least one measurement, feature, or characteristic of the heart sound signal.

In Example 4, the implantable medical device of Examples 1-3 optionally includes a cardiac sensor, coupled to the heart sound detector, configured to sense a cardiac signal. The heart sound detector of Examples 1-3 is also optionally configured to detect at least one heart sound of the heart sound signal using information from the cardiac signal.

In Example 5, the at least one heart sound of Examples 1-4 optionally includes at least one measurement, feature, characteristic, computation, or interval between at least one cardiac signal feature and at least one heart sound feature.

In Example 6, the system of Examples 1-5 optionally includes an implantable or external gating circuit, coupled to the cardiac sensor and the heart sound detector, wherein the gating circuit is configured to obtain a gated heart sound signal by gating the heart sound signal using information from the cardiac signal, and wherein the heart sound detector is configured to detect at least one heart sound of the gated heart sound signal.

In Example 7, the heart sound sensor of Examples 1-6 is optionally coupled to the cardiac sensor, wherein the heart sound sensor is enabled and disabled using the at least one cardiac signal feature.

In Example 8, the heart sound sensor of Examples 1-7 is optionally coupled to the respiration phase detector, wherein the heart sound sensor is enabled during the specified at least a portion of at least one phase of the respiration signal.

In Example 9, the system of Examples 1-8 optionally includes an implantable or external gating circuit, coupled to the respiration phase detector and the heart sound detector, wherein the gating circuit is configured to obtain a gated heart sound signal by gating the heart sound signal using information from the respiration phase detector, and wherein the heart sound detector is configured to detect at least one heart sound of the gated heart sound signal.

In Example 10, the system of Examples 1-9 optionally includes an external display, coupled to the processor, wherein the display is configured to display information from the processor.

In Example 11, the system of Examples 1-10 optionally includes an implantable or external analysis module, coupled to the processor, wherein the analysis module is configured to provide information about at least one cardiovascular status using information from the at least one heart sound trend.

In Example 12, the analysis module of Examples 1-11 is optionally configured to provide information about the at least one cardiovascular status using information from the at least one heart sound trend occurring during at least a portion of the at least one specified phase of the respiration signal.

In Example 13, the implantable medical device of Examples 1-12 optionally includes an implantable blood volume sensor, coupled to the processor, wherein the blood volume sensor is configured to detect information about a blood volume.

In Example 14, the analysis module of Examples 1-13 is optionally configured to provide information about the at least one cardiovascular status using information from the at least one heart sound trend and the blood volume sensor.

In Example 15, the analysis module of Examples 1-14 is optionally configured to provide information about the at least one cardiovascular status using information from the at least one heart sound trend occurring during at least a portion of at least one specified phase of the respiration signal and using information from the blood volume sensor.

In Example 16, a system includes means for sensing a respiration signal within a body, such as by using a respiration sensor to sense a respiration signal. The system also includes means for detecting at least one phase of the respiration signal, such as by using a respiration phase detector to detect at least one phase of the respiration signal. The system also includes means for sensing a heart sound signal within the body, such as by using a heart sound sensor to sense a heart sound signal. The system also includes means for detecting at least one heart sound of the heart sound signal, such as by using a heart sound detector to detect at least one heart sound of the heart sound signal. The system also includes means for automatically producing at least one heart sound trend, over at least a portion of at least one respiration cycle, wherein the at least one heart sound trend is indicative of at least one heart sound occurring during a specified at least a portion of at least one phase of the respiration signal, such as by using a processor, wherein the processor is configured to automatically produce at least one heart sound trend over at least a portion of at least one respiration cycle using the at least one heart sound, the at least one heart sound trend occurring during a specified at least a portion of at least one phase of the respiration signal.

In Example 17, a method includes sensing a respiration signal using an implanted respiration sensor. The method also includes detecting at least one phase of the respiration signal. The method also includes sensing a heart sound signal using an implanted heart sound sensor. The method also includes detecting at least one heart sound of the heart sound signal. The method also includes automatically producing at least one heart sound trend, over at least a portion of at least one respiration cycle, wherein the at least one heart sound trend is indicative of at least one heart sound occurring during a specified at least a portion of at least one phase of the respiration signal.

In Example 18, the automatically producing the at least one heart sound trend of Example 17 optionally includes automatically producing at least one measurement, feature, characteristic, computation, or interval of at least one heart sound.

In Example 19, the automatically producing at least one measurement, feature, characteristic, computation, or interval of at least one heart sound of Examples 17-18 optionally includes at least one of an automatically producing an amplitude of a heart sound, automatically producing a time interval between a first heart sound and a second heart sound, and automatically producing a normalized amplitude or interval of at least one measurement, feature, or characteristic of the heart sound signal.

In Example 20, the method of Examples 17-19 optionally includes sensing a cardiac signal using an implanted cardiac sensor. The detecting at least one heart sound of Examples 17-19 also optionally includes using information from the cardiac signal.

In Example 21, the automatically producing at least one heart sound trend of Examples 17-20 optionally includes automatically producing at least one measurement, feature, characteristic, computation, or interval between at least one cardiac signal feature and at least one heart sound feature.

In Example 22, the method of Examples 17-21 optionally includes gating the heart sound signal using a gating circuit to detect at least one heart sound, wherein the gating the heart sound signal includes using information from the cardiac signal.

In Example 23, the method of Examples 17-22 optionally includes enabling and disabling the heart sound sensor using the at least one cardiac signal feature.

In Example 24, the method of Examples 17-23 optionally includes enabling the heart sound sensor during at least one of the specified at least a portion of at least one phase of the respiration signal.

In Example 25, the method of Examples 17-24 optionally includes gating the heart sound signal to detect at least one heart sound, wherein the gating the heart sound signal includes gating the heart sound signal using information from the respiration signal.

In Example 26, the method of Examples 17-25 optionally includes displaying the at least one heart sound trend.

In Example 27, the method of Examples 17-26 optionally includes providing information about at least one cardiovascular status using information from the at least one heart sound trend.

In Example 28, the providing information about at least one cardiovascular status of Examples 17-27 optionally includes using information from the at least one heart sound trend occurring during specified different first and second phases of the respiration signal.

In Example 29, the method of Examples 17-28 optionally includes detecting information about a blood volume using an implanted blood volume sensor.

In Example 30, the providing information about the at least one cardiovascular status of Examples 17-29 optionally includes using information from the at least one heart sound trend and using information about the blood volume.

In Example 31, the providing information about the at least one cardiovascular status of Examples 17-30 optionally includes using information from the at least one heart sound trend occurring during specified different first and second phases of the respiration signal and using information about the blood volume.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, which are not necessarily drawn to scale, like numerals describe substantially similar components throughout the several views. Like numerals having different letter suffixes represent different instances of substantially similar components. The drawings illustrate generally, by way of example, but not by way of limitation, various embodiments discussed in the present document.

FIG. 1 illustrates generally an example of a system including an implantable medical device, which includes a respiration sensor, a respiration phase detector, a heart sound sensor, a heart sound detector, and a processor.

FIG. 2 illustrates generally an example of portions of a system including a heart sound detector and a cardiac sensor.

FIG. 3 illustrates generally an example of portions of a system including a heart sound detector, a gating circuit, and a cardiac sensor.

FIG. 4 illustrates generally an example of portions of a system including a heart sound sensor and a cardiac sensor.

FIG. 5 illustrates generally an example of portions of a system including a respiration phase detector and a heart sound sensor.

FIG. 6 illustrates generally an example of portions of a system including a respiration phase detector, a gating circuit, and a heart sound detector.

FIG. 7 illustrates generally an example of portions of a system including a processor and an external display.

FIG. 8 illustrates generally an example of portions of a system including a processor and an analysis module.

FIG. 9 illustrates generally an example of portions of a system including a processor, an analysis module, and a blood volume sensor.

FIG. 10 illustrates generally an example of a relationship between a respiration signal and a heart sound signal.

FIG. 11 illustrates generally an example of a relationship between the amplitude of a first heart sound (“S1 amplitude”) and the rate of pressure change (“dP/dt”), including a regression line and a correlation value (“R²”).

FIG. 12 illustrates generally an example of a relationship between the amplitude of a first heart sound (“S1 amplitude”) and the rate of pressure change (“dP/dt”), including an inspiratory first heart sound amplitude (“inspiratory S1 amplitude”) versus dP/dt, an inspiratory regression line, an inspiratory correlation value (“inspiratory R 2”), an expiratory first heart sound amplitude (“expiratory S1 amplitude”) versus dP/dt, an expiratory regression line, and an expiratory correlation value (“expiratory R²”).

FIG. 13 illustrates generally an example of a relationship between a first heart sound (“S1”) and a blood volume.

FIG. 14 illustrates generally an example of a method including sensing a respiration signal, detecting at least one phase of a respiration signal, sensing a heart sound signal, detecting at least one heart sound, and automatically producing at least one heart sound trend.

FIG. 15 illustrates generally an example of portions of a method including sensing a heart sound signal, sensing a cardiac signal, and detecting at least one heart sound.

FIG. 16 illustrates generally an example of portions of method including sensing a heart sound signal, sensing a cardiac signal, and gating the heart sound signal.

FIG. 17 illustrates generally an example of portions of a method including sensing a cardiac signal and enabling or disabling the heart sound sensor.

FIG. 18 illustrates generally an example of portions of a method including detecting at least one phase of a respiration signal and enabling or disabling the heart sound sensor.

FIG. 19 illustrates generally an example of portions of a method including sensing a heart sound signal, sensing a respiration signal, and gating the heart sound signal.

FIG. 20 illustrates generally an example of portions of a method including automatically producing at least one heart sound trend and displaying the at least one heart sound trend.

FIG. 21 illustrates generally an example of portions of a method including automatically producing at least one heart sound trend and providing information about at least one cardiovascular status.

FIG. 22 illustrates generally an example of portions of a method including automatically producing at least one heart sound trend, detecting information about a blood volume, and providing information about at least one cardiovascular status.

DETAILED DESCRIPTION

The following detailed description includes references to the accompanying drawings, which form a part of the detailed description. The drawings show, by way of illustration, specific embodiments in which the invention may be practiced. These embodiments, which are also referred to herein as “examples,” are described in enough detail to enable those skilled in the art to practice the invention. The embodiments may be combined, other embodiments may be utilized, or structural, logical and electrical changes may be made without departing from the scope of the present invention. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined by the appended claims and their equivalents.

In this document, the terms “a” or “an” are used, as is common in patent documents, to include one or more than one. In this document, the term “or” is used to refer to a nonexclusive or, unless otherwise indicated. The term “heart sound” is used to refer to the heart sound of a subject, and can include a first heart sound (“S1”), a second heart sound (“S2”), a third heart sound (“S3”), a fourth heart sound (“S4”), or any components thereof, such as the aortic component of S2 (“A2”), the pulmonic component of S2 (“P2”), or other sounds or vibrations associated with valve closures or fluid movement, such as a heart murmur, etc. Also, in this document, the terms “fist heart sound”, “second heart sound”, etc. are used to label a heart sound occurring in time, unless otherwise indicated, such as a first heart sound (“S1”), second heart sound (“S2”), etc. Furthermore, all publications, patents, and patent documents referred to in this document are incorporated by reference herein in their entirety, as though individually incorporated by reference. In the event of inconsistent usages between this document and those documents so incorporated by reference, the usage in the incorporated reference(s) should be considered supplementary to that of this document; for irreconcilable inconsistencies, the usage in this document controls.

Generally, inspiration results in a decreased intrathoracic pressure. The decreased intrathoracic pressure typically causes an increase in the venous blood return to the right side of the heart. The increased volume of blood entering the right-sided chambers of the heart can restrict the amount of blood entering the left-sided chambers of the heart. Typically, expiration results in an increased intrathoracic pressure. The increased intrathoracic pressure typically causes a decrease in the venous blood return to the right side of the heart. The decreased volume of blood entering the right-sided chambers of the heart can increase the amount of blood entering the left-sided chambers of the heart.

Detection of heart sounds during a particular phase or portion of the respiration cycle can result in an improved signal to noise ratio or correlation of the heart sound signal, generally due to the reduction in variability of the heart sound normally caused by respiration. An example of an improved correlation can be seen from FIG. 11 to FIG. 12. Further, noise from respiratory events, such as apnea, can be eliminated to improve certain diagnostic capabilities, such as heart failure diagnostics.

The detection of heart sounds during a particular phase or portion of the respiration cycle can also be used to obtain useful information, such as a slope of the Frank-Starling curve (the rate of change of at least one measurement, feature, characteristic, computation, or interval of at least a portion of at least one heart sound over the rate of change of blood volume), a comparison of heart sounds obtained during inspiration and expiration, etc. Such diagnostic information can be used to determine information about at least one cardiovascular status, including heart failure, cardiac performance, ventricular performance, ventricular failure, atrial performance, ischemia, myocardial infarction, pulmonary stenosis, atrial septal defects, etc.

FIG. 1 illustrates generally an example of a system 100 including an implantable medical device 105, which includes a respiration sensor 110, a respiration phase detector 115, a heart sound sensor 120, a heart sound detector 125, and a processor 130. In other examples, the respiration phase detector 115, the heart sound detector 125, or the processor 130, can be an implantable component external to the implantable medical device 105, or can be an external component. In other examples, some or all of the functionality of the respiration phase detector 115, or the heart sound detector 125, can be implemented in the processor 130.

In this example, the respiration sensor 110 is configured to sense a respiration signal of a subject. The respiration signal can include any signal indicative of the respiration of the subject, such as inspiration, expiration, or any combination, permutation, or component of the respiration of the subject. The respiration sensor 110 can be configured to produce a respiration signal, such as an electrical or optical respiration signal, that includes information about the respiration of the subject. In certain examples, the respiration sensor 110 can include an implantable sensor including at least one of an accelerometer, an impedance sensor, and a pressure sensor.

In an example, the respiration sensor 110 can include an accelerometer configured to sense an acceleration signal indicative of a cyclical variation indicative of respiration, such as that disclosed in the commonly assigned Kadhiresan et al. U.S. Pat. No. 5,974,340 entitled “APPARATUS AND METHOD FOR MONITORING REPSIRATORY FUNCTION IN HEART FAILURE PATIENTS TO DETERMINE EFFICACY OF THERAPY,” (herein “Kadhiresan et al. '340”) which is hereby incorporated by reference in its entirety, including its disclosure of using an accelerometer to detect respiration. In another example, the respiration sensor 110 can include a vibration sensor, such as that disclosed in the commonly assigned Hatlestad et al. U.S. Pat. No. 6,949,075 entitled “APPARATUS AND METHOD FOR DETECTING LUNG SOUNDS USING AN IMPLANTED DEVICE,” (herein “Hatlestad et al. '075”) which is hereby incorporated by reference in its entirety, including its disclosure of using a vibration sensor to detect respiration. In other examples, other accelerometer configurations can be used to sense the respiration signal.

In another example, the respiration sensor 110 can include an impedance sensor configured to sense an impedance signal indicative of respiration, such as that disclosed in the commonly assigned Kadhiresan et al. '340, incorporated by reference in its entirety. In another example, the respiration sensor 110 can include a transthoracic impedance sensor, such as that disclosed in the commonly assigned Hartley et al. U.S. Pat. No. 6,076,015 entitled “RATE ADAPTIVE CARDIAC RHYTHM MANAGEMENT DEVICE USING TRANSTHROACIC IMPEDANCE,” which is hereby incorporated by reference in its entirety, including its disclosure of using a thoracic impedance sensor to detect respiration. In other examples, other impedance sensor configurations can be used to sense the respiration signal.

In another example, the respiration sensor 110 can include a pressure sensor configured to sense a pressure signal indicative of respiration, such as that disclosed in the commonly assigned Hatlestad et al. '075, incorporated by reference in its entirety, including its disclosure of sensing a pressure signal indicative of respiration. In other examples, other pressure sensor configurations, such as a pulmonary artery pressure sensor, a ventricular pressure sensor, a thoracic pressure sensor, etc., can be used to sense a respiration signal.

In the example of FIG. 1, the respiration phase detector 115 is coupled to the respiration sensor 110. The respiration phase detector 115 can be configured to receive the respiration signal from the respiration sensor 110. Generally, the respiration phase detector 115 can be configured to detect at least a particular portion of at least one phase of the respiration signal. In certain examples, this includes at least portion of at least one of an inspiration, an expiration, a transition between inspiration and expiration, and a transition between expiration and inspiration.

In this example, the heart sound sensor 120 can be configured to sense a heart sound signal of a subject. The heart sound signal can include any signal indicative of at least a portion of at least one heart sound of the subject. A heart sound of the subject can include an audible or mechanical noise or vibration indicative of blood flow through the heart or valve closures of the heart. A heart sound of the subject can include S1, S2, S3, S4, or any components thereof, such as A2, P2, etc. The heart sound sensor 120 can be configured to produce a heart sound signal, such as an electrical or optical heart sound signal, that includes information about the heart sound signal of the subject. The heart sound sensor 120 can include any device configured to sense the heart sound signal of the subject. In certain examples, the heart sound sensor 120 can include an implantable sensor including at least one of an accelerometer, an acoustic sensor, a microphone, etc.

In an example, the heart sound sensor 120 can include an accelerometer configured to sense an acceleration signal indicative of the heart sound of the subject, such as that disclosed in the commonly assigned Carlson et al. U.S. Pat. No. 5,792,195 entitled “ACCELERATION SENSED SAFE UPPER RATE ENVELOPE FOR CALCULATING THE HEMODYNAMIC UPPER RATE LIMIT FOR A RATE ADAPTIVE CARDIAC RHYTHM MANAGEMENT DEVICE,” which is hereby incorporated by reference in its entirety including its disclosure of accelerometer detection of heart sounds, or such as that disclosed in the commonly assigned Siejko et al. U.S. patent application Ser. No. 10/334,694, entitled “METHOD AND APPARATUS FOR MONITORING OF DIASTOLIC HEMODYNAMICS,” filed Dec. 30, 2002 (Attorney Docket No. 279.576US1) (herein “Siejko et al. '694”), which is hereby incorporated by reference in its entirety including its disclosure of accelerometer detection of heart sounds. In other examples, other accelerometer or acceleration sensor configurations can be used to sense the heart sound signal.

In another example, the heart sound sensor 120 can include an acoustic sensor configured to sense an acoustic energy indicative of the heart sound of the subject, such as that disclosed in the commonly assigned Siejko et al. '694, incorporated by reference in its entirety. In other examples, other acoustic sensor or microphone configurations can be used to sense the heart sound signal.

In the example of FIG. 1, the heart sound detector 125 is coupled to the heart sound sensor 120. The heart sound detector 125 can be configured to receive the heart sound signal from the heart sound sensor 120. Generally, the heart sound detector 125 can be configured to detect at least one measurement, feature, characteristic, computation, or interval of at least a portion of at least one heart sound. In certain examples, this includes at least one of an amplitude of a heart sound, a magnitude of a heart sound, a total energy of a heart sound, an interval between one heart sound feature and another heart sound feature, at least one heart sound characteristic normalized by at least one other heart sound characteristic, etc. (e.g., an amplitude or magnitude of S1, an amplitude or magnitude of S2, an amplitude or magnitude of S3, an amplitude or magnitude of S4, the existence of a split-S2, a split-S2 time interval, a time interval between S1 and S2 (“S1-S2 time interval”), a time interval between S2 and S3 (“S2-S3 time interval”), a characteristic of S3 normalized by a characteristic of S1, etc.).

In the example of FIG. 1, the processor 130 is coupled to the respiration phase detector 115 and the heart sound detector 125. The processor 130 can be configured to receive the at least a portion of at least one phase of the respiration signal from the respiration phase detector 115, and the at least a portion of the at least one heart sound or component of the heart sound signal from the heart sound detector 125. Generally, the processor 130 can be configured to automatically produce at least one heart sound trend using information from the respiration phase detector 115 and the heart sound detector 125.

Generally, a heart sound trend can include an index of information about at least one measurement, feature, characteristic, computation, or interval of at least a portion of at least one heart sound. In this example, the heart sound trend includes an index of information about at least one measurement, feature, characteristic, computation, or interval of at least a portion of at least one heart sound arranged, sorted, or otherwise indexed using the at least a portion of the at least one phase of the respiration signal. Illustrative examples of heart sound trends arranged, sorted, or otherwise indexed using the at least a portion of the at least one phase of the respiration signal include an index of at least one S1 amplitude during inspiration, an index of at least one S1 amplitude during expiration, an index of at least one S2 amplitude during inspiration, an index of the rate of change of S1 amplitude (“ΔS1”) during inspiration, an index of at least one S1-S2 time interval during inspiration, a ratio or a relative measurement or a comparison between at least one S1 amplitude during inspiration and at least one S1 amplitude during expiration, etc.

FIG. 2 illustrates generally an example of portions of a system 200 including a heart sound detector 125 and a cardiac sensor 135. In certain examples, the heart sound detector 125, or the cardiac sensor 135, can be included in the implantable medical device 105. In other examples, the heart sound detector 125 can be an implantable component external to the implantable medical device 105, or can be an external component. In an example, some or all of the functionality of the heart sound detector 125 can be implemented in the processor 130.

In this example, the cardiac sensor 135 can be configured to sense a cardiac signal of a subject. The cardiac signal can include any signal indicative of the electrical or mechanical cardiac activity of the heart, e.g., an electrocardiogram (“ECG”) signal, an impedance signal, an acceleration signal, etc. The cardiac sensor 135 can be configured to produce a cardiac signal, such as an electrical or optical cardiac signal, that includes information about the cardiac signal of the subject. The cardiac sensor 135 can include any device configured to sense the cardiac activity of the subject. In certain examples, the cardiac sensor 135 can include an intrinsic cardiac signal sensor, such as one or more than one electrode or lead to sense one or more than one depolarization, or a mechanical sensor, such as an impedance sensor or an accelerometer to sense one or more than one contraction.

In the example of FIG. 2, the heart sound detector 125 is coupled to the cardiac sensor 135. The heart sound detector 125 can be configured to receive the cardiac signal from the cardiac sensor 135 or a heart sound signal from the heart sound sensor 120. In this example, the heart sound detector 125 can be configured to detect at least one measurement, feature, characteristic, computation, or interval of at least a portion of at least one heart sound using the heart sound sensor 120 and the cardiac sensor 135.

Generally, the at least one measurement, feature, characteristic, computation, or interval of at least a portion of at least one heart sound includes at least one measurement, feature, characteristic, computation, or interval between at least one cardiac signal feature and at least one heart sound signal feature. Typically, the at least one cardiac signal feature can include at least one feature or component of an ECG signal, e.g., at least one component of a P-wave, at least one component of a Q-wave, at least one component of a R-wave, at least one component of a S-wave, at least one component of a T-wave, or any combination or permutation of features or components of the ECG signal, or any mechanical cardiac features of a pressure signal or acceleration signal indicative of the cardiac activity of a subject. In certain examples, the at least one measurement, feature, characteristic, computation, or interval between at least one cardiac signal feature and at least one heart sound signal feature includes a systolic time interval (“STI”) (e.g., a total electromechanical systole (“Q-S2”), a pre-ejection phase (“PEP”), a left-ventricular ejection time (“LVET”), an isovolumetric contraction time (“ICT”), a S1-S2 time interval, etc.), a long Q-S1 time interval, a R-S1 time interval, R-S2 interval, etc.

FIG. 3 illustrates generally an example of portions of a system 300 including a heart sound detector 125, a gating circuit 126, and a cardiac sensor 135. In certain examples, the heart sound detector 125, the gating circuit 126, or the cardiac sensor 135, can be included in the implantable medical device 105. In other examples, the heart sound detector 125, or the gating circuit 126, can be an implantable component external to the implantable medical device 105, or can be an external component. In other examples, some or all of the functionality of the heart sound detector 125, or the gating circuit 126, can be implemented in the processor 130.

Generally, the cardiac sensor 135 can be configured to sense a cardiac signal of a subject. In this example, the gating circuit 126 is coupled to the cardiac sensor 135 and the heart sound detector 125. The gating circuit 126 can be configured to receive the cardiac signal from the cardiac sensor 135, or the heart sound signal from the heart sound sensor 120 or the heart sound detector 125. The gating circuit 126 can be configured to obtain a gated heart sound signal, such as by gating the heart sound signal using information from the cardiac signal. Typically, the gating circuit 126 gates the heart sound signal using at least one cardiac signal feature of the cardiac signal to detect at least a portion of at least one heart sound. In an example, the gated heart sound signal can include at least a portion of at least one heart sound, such as the S1, S2, etc.

In an example, the gating circuit 126 can be configured to implement a detection window to detect at least a portion of at least one heart sound, such as that disclosed in the commonly assigned Zhu et al. U.S. Pat. No. 6,650,940 entitled “ACCELEROMETER-BASED HEART SOUND DETECTION FOR AUTOCAPTURE,” which is hereby incorporated by reference in its entirety, including its disclosure of using a detection window to detect at least one portion of a heart sound. In other examples, other gating circuit configurations can be used to detect at least a portion of at least one heart sound.

FIG. 4 illustrates generally an example of portions of a system 400 including a heart sound sensor 120 and a cardiac sensor 135. In certain examples, the heart sound sensor 120, or the cardiac sensor 135, can be included in the implantable medical device 105.

In the example of FIG. 4, the heart sound sensor 120 can be enabled or disabled using information from the cardiac sensor 135. In an example, the heart sound sensor 120 can be enabled during at least a portion of at least one cardiac cycle. The at least a portion of the at least one cardiac cycle can be detected using information from the cardiac signal. In another example, the heart sound sensor 120 can be enabled for a period of time using information from the cardiac sensor 135, such as being enabled for at least a portion of at least one cardiac cycle every ten cardiac cycles, being enabled for at least a portion of at least one cardiac cycle every one hundred cardiac cycles, etc., or such as being enabled for at least a portion of at least one cardiac cycle once or more than once per hour, day, week, etc. In other examples, the heart sound sensor 120 can be enabled during a cardiac event, such as an ischemic event, a myocardial infarction event, an increased or decreased heart rate, etc.

FIG. 5 illustrates generally an example of portions of a system 500 including a respiration phase detector 115 and a heart sound sensor 120. In certain examples, the respiration phase detector 115, or the heart sound sensor 120, can be included in the implantable medical device 105. In other examples, the respiration phase detector 115 can be an implantable component external to the implantable medical device 105, or can be an external component. In an example, some or all of the functionality of the respiration phase detector 115 can be implemented in the processor 130.

In the example of FIG. 5, the heart sound sensor 120 can be enabled or disabled using information from the respiration phase detector 115. In an example, the heart sound sensor 120 can be enabled during at least a portion of at least one respiration phase. The at least a portion of the at least one respiration phase can be detected using information from the respiration sensor. In another example, the heart sound sensor 120 can be enabled for a period of time using information from the respiration phase detector 115, such as being enabled for at least a portion of at least one respiration phase or cycle every ten respiration phases or cycles, being enabled for at least a portion of at least one respiration phase or cycle every one hundred respiration phases or cycles, etc., or such as being enabled for at least a portion of at least one respiration phase or cycle once or more than once per hour, day, week, etc. In other examples, the heart sound sensor 120 can be enabled during a respiration event, such as an apnea event, an increased or decreased respiratory rate, etc.

FIG. 6 illustrates generally an example of portions of a system 600 including a respiration phase detector 115, a gating circuit 126, and a heart sound detector 125. In certain examples, the respiration phase detector 115, the gating circuit 126, or the heart sound detector 125, can be included in the implantable medical device 105, can be an implantable component external to the implantable medical device 105, or can be an external component. In other examples, some or all of the functionality of the respiration phase detector 115, the gating circuit 126, or the heart sound detector 125, can be implemented in the processor 130.

Generally, the respiration phase detector 115 can be configured to detect at least a portion of at least one phase of a respiration signal of a subject. In this example, the gating circuit 126 is coupled to the respiration phase detector 115 and the heart sound detector 125. The gating circuit 126 can be configured to receive the at least a portion of at least one phase of the respiration signal from the respiration phase detector 115, or the heart sound signal from the heart sound sensor 120 or the heart sound detector 125. The gating circuit 126 can be configured to obtain a gated heart sound signal, such as by gating the heart sound signal using information from the respiration signal. Typically, the gating circuit 126 gates the heart sound signal using at least one respiration feature of the respiration signal to detect at least a portion of at least one heart sound occurring during at least a portion of at least one phase of the respiration signal. In an example, the gated heart sound signal can include at least a portion of at least one heart sound, such as the S1, S2, etc., occurring during at least a portion of at least one phase of the respiration signal, such as at least a portion of inspiration, expiration, or the transition from inspiration to expiration or expiration to inspiration.

FIG. 7 illustrates generally an example of portions of a system 700 including a processor 130 and an external display 140. In certain examples, the processor 130 can be included in the implantable medical device 105, can be an implantable component external to the implantable medical device 105, or can be an external component.

Generally, the processor 130 can be configured to automatically produce at least one heart sound trend using information from a respiration signal of a subject and a heart sound signal of the subject. In this example, the external display 140 is coupled to the processor 130. The external display 140 can be configured to receive information from the processor 130. The external display 140 can be configured to display information from the processor 130, such as information about the at least one heart sound trend. In certain examples, the external display can include an external programmer, a remote patient monitoring system, a computing device, such as a personal digital assistant (“PDA”), a notebook computer, a desktop computer, a cellular phone, or other computing device, or an external display, such as a liquid crystal display (“LCD”) or other external display. In an example, the external display 140 can include a memory to store information from the processor 130. In another example, the external display 140 can be configured to further process the information received from the processor 130. The external display 140 can also be configured to communicate to an external device, such as an external repeater. The external repeater can be configured to communicate, such as by an e-mail or other communication, to a user, such as a physician or other caregiver, or a subject.

FIG. 8 illustrates generally an example of portions of a system 800 including a processor 130 and an analysis module 145. In certain examples, the processor 130, or the analysis module 145, can be included in the implantable medical device 105, can be an implantable component external to the implantable medical device 105, or can be an external component. In an example, some or all of the functionality of the analysis module 145 can be implemented in the processor 130.

Generally, the processor 130 can be configured to automatically produce at least one heart sound trend using information from a respiration signal and a heart sound signal of a subject. In this example, the analysis module 145 is coupled to the processor 130. The analysis module 145 can be configured to receive information from the processor 130. The analysis module 145 can be configured to provide information about at least one cardiovascular status using information from the at least one heart sound trend.

FIG. 9 illustrates generally an example of portions of a system 900 including a processor 130, an analysis module 145, and a blood volume sensor 150. In certain examples, the processor 130, the analysis module 145, or the blood volume sensor 150, can be included in the implantable medical device 105. In other examples, the processor 130, or the analysis module 145, can be an implantable component external to the implantable medical device 105, or can be an external component. In an example, some or all of the functionality of the analysis module 145 can be implemented in the processor 130.

In this example, the blood volume sensor 150 is coupled to the processor 130. Generally, the blood volume sensor 150 can be configured to sense a blood volume of a subject. In an example, the blood volume can include a stroke volume, a cardiac output, etc. Additionally or alternatively, the blood volume of the subject can be determined, estimated, or correlated using a respiration signal, such as a minute ventilation (“MV”) signal, a tidal volume signal, or other respiration signal, an impedance signal, such as a transthoracic impedance signal or other impedance signal, or a pressure signal, such as a thoracic pressure signal or other pressure signal. The blood volume sensor 150 can include any sensor configured to sense the blood volume of the subject.

In an example, the blood volume sensor 150 can include a MV sensor configured to sense a ventilation signal indicative of the blood volume of the subject, such as that disclosed in the commonly assigned Larsen et al. U.S. Pat. No. 6,868,346 entitled “MINUTE VENTILATION SENSOR WITH AUTOMATIC HIGH PASS FILTER ADJUSTMENT,” which is hereby incorporated by reference in its entirety, including its disclosure of an MV sensor that senses a ventilation signal. In another example, the blood volume sensor 150 can include a MV sensor configured to sense a ventilation signal indicative of the ventilation of the subject, such as that disclosed in the commonly assigned Yonce U.S. Pat. No. 6,741,886 entitled “ECG SYSTEM WITH MINUTE VENTILATION DETECTOR,” which is hereby incorporated by reference in its entirety, including its disclosure of an MV sensor and ventilation sensing.

In yet another example, the blood volume sensor 150 can include at least one of a MV sensor configured to sense a ventilation signal indicative of the blood volume of the subject and an impedance sensor configured to sense an impedance signal indicative of the blood volume of a subject, such as that disclosed in the commonly assigned Hartley et al. U.S. Pat. No. 6,076,015 “RATE ADAPTIVE CARDIAC RHYTHM MANAGEMENT DEVICE USING TRANSTHORACIC IMPEDANCE,” Hartley et al. U.S. Pat. No. 6,161,042 “RATE ADAPTIVE CARDIAC RHYTHM MANAGEMENT DEVICE USING TRANSTHORACIC IMPEDANCE,” or Hartley et al. U.S. Pat. No. 6,463,326 “RATE ADAPTIVE CARDIAC RHYTHM MANAGEMENT DEVICE USING TRANSTHORACIC IMPEDANCE,” which are hereby incorporated by reference in their entirety including their disclosure of using an MV sensor to sense a ventilation signal indicative of blood volume and an impedance sensor to sense an impedance signal indicative of blood volume. In other examples, other MV sensor configurations can be used to sense a blood volume.

In another example, the blood volume sensor 150 can include an impedance sensor configured to sense an impedance signal indicative of the blood volume of the subject, such as that disclosed in the commonly assigned Salo et al. U.S. Pat. No. 5,190,035 “BIOMEDICAL METHOD AND APPARATUS FOR CONTROLLING THE ADMINISTRATION OF THERAPY TO A PATIENT IN RESPONSE TO CHANGES IN PHYSIOLOGICAL DEMAND,” which is hereby incorporated by reference in its entirety including its disclosure of a blood volume sensor.

In yet another example, the blood volume sensor 150 can include an impedance sensor configured to sense an impedance signal indicative of the blood volume of the subject, such as that disclosed in the commonly assigned Citak et al. U.S. Pat. No. 4,773,401 “PHYSIOLOGIC CONTROL OF PACEMAKER RATE USING PRE-EJECTION INTERVAL AS THE CONTROLLING PARAMETER,” which is hereby incorporated by reference in its entirety including its disclosure of detecting an impedance signal indicative of blood volume. In other examples, other impedance sensor configurations can be used to sense a blood volume.

The blood volume sensor 150, like the heart sound sensor 120, can be gated, such as by using information from the cardiac sensor 135, the respiration sensor 110, or the respiration phase detector 115. Further, the blood volume sensor, like the heart sound sensor 120, can be enabled or disabled, such as by using information from the cardiac sensor 135, the respiration sensor 110, or the respiration phase detector 115.

Generally, the processor 130 can be configured to automatically produce at least one heart sound trend using information from a respiration signal and a heart sound signal of a subject. In this example, the processor 130 can be configured to receive a blood volume signal from the blood volume sensor 150.

In the example of FIG. 9, the analysis module 145 is coupled to the processor 130. The analysis module 145 can be configured to receive information from the processor 130, such as the at least one heart sound trend and the blood volume signal. The analysis module 145 can be configured to provide information about at least one cardiovascular status using information from the at least one heart sound trend and the blood volume signal.

FIG. 10 illustrates generally an example 1000 of a relationship between a respiration signal 1005, including a inspiratory respiration signal component 1006 and an expiratory respiration signal component 1007, and a heart sound signal 1010, including an inspiratory heart sound signal component 1011 and an expiratory heart sound signal component 1012.

Typically, the heart sound signal varies with respiration. In the example of FIG. 10, the heart sound signal 1010 generally has a larger magnitude during the expiratory respiration signal component 1007 of the respiration signal 1005, such as at the expiratory heart sound signal component 1012, than during the inspiratory respiration signal component 1006 of the respiration signal 1005, such as at the inspiratory heart sound signal component 1011.

FIG. 11 illustrates generally an example 1100 of a relationship between the amplitude of a first heart sound (“S1 amplitude”) 1101 and the rate of pressure change (“dP/dt”) 1102, including a regression line 1105 and a correlation value (“R²”) 1110.

Regression analysis is generally used to determine the relationship between two or more measurements. A regression line of a set of data is typically the line of best fit, or the line that comes closest to all data points in the set. Correlation is generally the degree to which the two or more measurements are similar or related. A higher value of correlation corresponds to a higher degree of relation. Cleaner and more accurate signals typically have a higher value of correlation.

In the example of FIG. 11, S1 amplitude 1101 includes S1 amplitude during inspiration and expiration. In this example, the regression line 1105 is the line of best fit for the data of S1 amplitude 1101 versus dP/dt 1102. The R² 1110 for the S1 amplitude 1101 versus dP/dt 1102 is 0.4209.

FIG. 12 illustrates generally an example 1200 of a relationship between the amplitude of a first heart sound (“S1 amplitude”) 1201 and the rate of pressure change (“dP/dt”) 1202, including an inspiratory first heart sound amplitude (“inspiratory S1 amplitude”) 1205 versus dP/dt 1202, an inspiratory regression line 1206, an inspiratory correlation value (“inspiratory R²”) 1207, an expiratory first heart sound amplitude (“expiratory S1 amplitude”) 1210 versus dP/dt 1202, an expiratory regression line 1211, and an expiratory correlation value (“expiratory R²”) 1212.

Generally, FIG. 12 illustrates that detecting heart sounds during the different phases of the respiration signal, such as inspiration, expiration, etc., has a higher correlation than other modes of detection, such as that shown in example 1100. In the example of FIG. 12, inspiratory S1 amplitude 1205 includes S1 amplitude during inspiration. In this example, the inspiratory regression line 1206 is the line of best fit for the data of inspiratory S1 amplitude 1205 versus dP/dt 1202. The inspiratory R² 1207 for the inspiratory S1 amplitude 1205 versus dP/dt 1202 is 0.5719. The expiratory regression line 1211 is the line of best fit for the data of expiratory S1 amplitude 1210 versus dP/dt 1202. The expiratory R² 1212 for the expiratory S1 amplitude 1210 versus dP/dt 1202 is 0.8581.

FIG. 13 illustrates generally an example 1300 of a relationship between a first heart sound (“S1”) 1301 and a blood volume 1302, including an increased performance curve 1305, a normal curve 1310, and a heart failure curve 1315.

The relationship between S1 1301 and the blood volume 1302 of the example 1300 is sometimes called the Frank-Starling curve. Generally, the Frank-Starling curve can be used to measure cardiac performance. The Frank-Starling curve typically demonstrates that performance of a failing heart can improve with either an increase in contractility or a decrease in afterload. Normal heart function is typically associated with adequate tissue perfusion without pulmonary congestion. Heart failure generally results in a downward shift of the Frank-Starling curve, and concurrently a decreased operating slope of the Frank-Starling curve. Typically, this downward shift or decreased operating slope can result in hypoperfusion, pulmonary congestion, etc.

FIG. 14 illustrates generally an example of a method 1400 including sensing a respiration signal, detecting at least one phase of a respiration signal, sensing a heart sound signal, detecting at least one heart sound, and automatically producing at least one heart sound trend.

At 1405, a respiration signal is sensed. The respiration signal can include any signal indicative of the respiration of a subject, such as inspiration, expiration, or any combination, permutation, or component of the respiration of the subject. In an example, the respiration signal can be sensed using the respiration sensor 110.

At 1410, at least one phase of a respiration signal is detected. The at least one phase of the respiration signal can be detected using the respiration signal. In certain examples, the at least one phase of the respiration signal includes at least a portion of at least one of an inspiration, an expiration, a transition between inspiration and expiration, a transition between expiration and inspiration, etc. In certain examples, an inspiration, an expiration, the transitions between inspiration and expiration, etc., can be determined using the respiration signal, such as by differentiating the respiration signal to attain the slope of the respiration signal, by detecting peaks and valleys of the respiration signal, or by using other filtering methods or signal characteristics. In an example, the at least one phase of the respiration signal can be detected using the respiration phase detector 115.

In an example, the at least one phase of the respiration signal includes an inspiration of one respiration cycle. A respiration cycle can include one full inspiration and expiration, one full expiration and inspiration, or any permutation or combination of a full inspiration and a full expiration. In other examples, the at least one phase of the respiration signal includes an expiration of one respiration cycle, a portion of an inspiration of one respiration cycle, a portion of an expiration of one respiration cycle, a portion of an inspiration and an expiration of one respiration cycle, a portion of an inspiration or an expiration of more than one respiration cycle, a portion of an inspiration and an expiration of more than one respiration cycle, etc.

At 1415, a heart sound signal is sensed. The heart sound signal can include any signal indicative of at least a portion of at least one heart sound of the subject. A heart sound of the subject can include an audible or mechanical noise or vibration indicative of blood flow through a heart or one or more than one valve closure of the heart. This noise or vibration can include S1, S2, S3, S4, or any components thereof, such as A2, P2, etc. In an example, the heart sound signal can be sensed using the heart sound sensor 120.

At 1420, at least one heart sound is detected. The at least one heart sound can be detected using the heart sound signal. Generally, the at least one heart sound includes at least one measurement, feature, characteristic, computation, or interval of at least a portion of the heart sound signal. In certain examples, the at least one measurement, feature, characteristic, computation, or interval of the at least a portion of the heart sound signal includes at least one of an amplitude of a heart sound, a magnitude of a heart sound, a total energy of a heart sound, an interval between one heart sound feature and another heart sound feature, at least one heart sound characteristic normalized by at least one other heart sound characteristic, etc. (e.g., an amplitude or magnitude of S1, an amplitude or magnitude of S2, an amplitude or magnitude of S3, an amplitude or magnitude of S4, the existence of a split-S2, a split-S2 time interval, a S1-S2 time interval, a S2-S3 time interval, a characteristic of S3 normalized by a characteristic of S1, etc.). In an example, the at least one heart sound can be detected using the heart sound detector 125.

At 1425, at least one heart sound trend is automatically produced. The at least one heart sound trend can be automatically produced using the at least one phase of the respiration signal, detected at 1410, and the at least one heart sound, detected at 1420. At 1425, the at least one heart sound trend includes an index of information about at least one measurement, feature, characteristic, computation, or interval of at least a portion of at least one heart sound arranged, sorted, or otherwise indexed using the at least a portion of the at least one phase of the respiration signal. In an example, the at least one heart sound trend can be automatically produced using the processor 130.

FIG. 15 illustrates generally an example of portions of a method 1500 including sensing a heart sound signal, sensing a cardiac signal, and detecting at least one heart sound.

At 1515, a heart sound signal is sensed. The heart sound signal can include any signal indicative of at least a portion of at least one heart sound of the subject. In an example, the heart sound signal can be sensed using the heart sound sensor 120.

At 1516, a cardiac signal is sensed. The cardiac signal can include any signal indicative of the electrical or mechanical cardiac activity of a heart. In an example, the cardiac signal can be sensed using the cardiac sensor 135.

At 1520, at least one heart sound is detected. The at least one heart sound can be detected using the heart sound signal and the cardiac signal. Generally, the at least one heart sound can include at least one measurement, feature, characteristic, computation, or interval between at least one cardiac signal feature and at least one heart sound signal feature. Typically, the at least one cardiac signal feature can include at least one feature or component of an ECG signal, e.g., at least one component of a P-wave, at least one component of a Q-wave, at least one component of a R-wave, at least one component of a S-wave, at least one component of a T-wave, or any combination or permutation of features or components of the ECG signal, or any mechanical cardiac features of a pressure signal or acceleration signal indicative of the cardiac activity of a subject. In certain examples, the at least one measurement, feature, characteristic, computation, or interval between at least one cardiac signal feature and at least one heart sound signal feature includes a STI (e.g., Q-S2, PEP, LVET, ICT, etc.), a long Q-S1 time interval, a R-S1 time interval, R-S2 interval, etc. In an example, the at least one heart sound can be detected using the heart sound sensor 120.

FIG. 16 illustrates generally an example of portions of method 1600 including sensing a heart sound signal, sensing a cardiac signal, and gating the heart sound signal.

At 1615, a heart sound signal is sensed. The heart sound signal can include any signal indicative of at least a portion of at least one heart sound of the subject. In an example, the heart sound signal can be sensed using the heart sound sensor 120.

At 1616, a cardiac signal is sensed. The cardiac signal can include any signal indicative of the electrical or mechanical cardiac activity of a heart. In an example, the cardiac signal can be sensed using the cardiac sensor 135.

At 1635, the heart sound signal is gated. The heart sound signal can be gated using information from the cardiac signal. Typically, the heart sound signal can be gated in order to detect at least a portion of at least one heart sound, such as S1, S2, etc. In an example, the heart sound signal can be gated using the gating circuit 126.

In an example, at 1635, the heart sound signal is gated using a first feature of the cardiac signal and a second feature of the cardiac signal. In another example, at 1635, the heart sound signal is gated using a first feature of the cardiac signal and a time interval. In an example, the time interval has a duration from 100-300 milliseconds.

FIG. 17 illustrates generally an example of portions of a method 1700 including sensing a cardiac signal and enabling or disabling the heart sound sensor.

At 1716, a cardiac signal is sensed. The cardiac signal can include any signal indicative of the electrical or mechanical cardiac activity of a heart. In an example, the cardiac signal can be sensed using the cardiac sensor 135.

At 1740, the heart sound sensor is enabled or disabled. Generally, enabling or disabling the heart sound sensor can reduce power consumption. The heart sound sensor can be enabled or disabled using information from the cardiac signal, such as at least one specific cardiac feature. In an example, the heart sound sensor can be enabled or disabled during at least a portion of at least one cardiac cycle, where the cardiac cycle is determined using the cardiac signal. In other examples, the heart sound sensor can be enabled or disabled during at least a portion of at least one cardiac cycle during at least one specific cardiac cycle or time period, such as during at least a portion of at least one cardiac cycle every fifth cardiac cycle, or during at least a portion of at least one cardiac cycle for ten consecutive cardiac cycles once per hour, etc. In other examples, the heart sound sensor can be enabled during specific cardiac events, such as an ischemic event, a myocardial infarction event, etc., or disabled during specific cardiac events, such as during normal cardiac function.

FIG. 18 illustrates generally an example of portions of a method 1800 including detecting at least one phase of a respiration signal and enabling or disabling the heart sound sensor.

At 1810, at least one phase of a respiration signal is detected. The at least one phase of the respiration signal can be detected using the respiration signal. In an example, the at least one phase of the respiration signal can be detected using the respiration phase detector 115.

At 1840, the heart sound sensor is enabled or disabled. Generally, enabling or disabling the heart sound sensor can reduce power consumption. The heart sound sensor can be enabled or disabled using information from the respiration signal. In an example, the heart sound sensor can be enabled or disabled during at least a portion of at least one phase of the respiration signal. In another example, the heart sound sensor can be enabled or disabled during at least a portion of at least one phase of the respiration signal during at least one specific respiration cycle or time period, such as during inspiration every fifth respiration cycle, or during inspiration for ten consecutive respiration cycles once per hour, etc. In other examples, the heart sound sensor can be enabled during specific respiratory events, such as an apnea event, an increased or decreased respiratory rate, etc., or disabled during specific respiratory events, such as during normal respiratory function.

FIG. 19 illustrates generally an example of portions of a method 1900 including sensing a heart sound signal, sensing a respiration signal, and gating the heart sound signal.

At 1905, a respiration signal is sensed. The respiration signal can include any signal indicative of the respiration of the subject, such as inspiration, expiration, or any combination, permutation, or component of the respiration of the subject. In an example, the respiration signal can be sensed using the respiration sensor 110.

At 1915, a heart sound signal is sensed. The heart sound signal can include any signal indicative of at least a portion of at least one heart sound of the subject. In an example, the heart sound signal can be sensed using the heart sound sensor 120.

At 1935, the heart sound signal is gated. The heart sound signal can be gated using information from the respiration signal. Typically, the heart sound signal can be gated in order to detect at least a portion of at least one heart sound, such as S1, S2, etc., during at least a portion of at least one phase of the respiration signal, such as inspiration, expiration, etc. In an example, the heart sound signal can be gated using the gating circuit 126.

FIG. 20 illustrates generally an example of portions of a method 2000 including automatically producing at least one heart sound trend and displaying the at least one heart sound trend.

At 2025, at least one heart sound trend is automatically produced. The at least one heart sound trend can be automatically produced using at least one phase of a respiration signal and at least one heart sound. The at least one heart sound trend includes an index of information about at least one measurement, feature, characteristic, computation, or interval of at least a portion of at least one heart sound arranged, sorted, or otherwise indexed using at least a portion of at least one phase of the respiration signal. In an example, the at least one heart sound trend can be automatically produced using the processor 130.

At 2045, at least one heart sound trend is displayed. The at least one heart sound trend can be displayed using an external display, such as an LCD display or other external display, an external programmer, a remote patient monitoring system, a computing device, such as a personal digital assistant (“PDA”), a notebook computer, a desktop computer, a cellular phone, or other computing devices. In an example, the at least one heart sound trend can be displayed using the external display 140.

FIG. 21 illustrates generally an example of portions of a method 2100 including automatically producing at least one heart sound trend and providing information about at least one cardiovascular status.

At 2125, at least one heart sound trend is automatically produced. The at least one heart sound trend can be automatically produced using at least one phase of a respiration signal and at least one heart sound. The at least one heart sound trend includes an index of information about at least one measurement, feature, characteristic, computation, or interval of at least a portion of at least one heart sound arranged, sorted, or otherwise indexed using at least a portion of at least one phase of the respiration signal. In an example, the at least one heart sound trend can be automatically produced using the processor 130.

At 2150, information about at least one cardiovascular status is provided. The information about the at least one cardiovascular status can be provided using information from the at least one heart sound trend. The information about at least one cardiovascular status can include information about heart failure, cardiac performance, ventricular performance, ventricular failure, atrial performance, ischemia, myocardial infarction, pulmonary stenosis, atrial septal defects, etc. In an example, the information about at least one cardiovascular status is provided using an analysis module 145.

Generally, S2 can include two components, A2 and P2. In an example, A2 and P2 timing and location are generally modulated by respiration. Typically, the aortic valve and pulmonic valve remain open longer during inspiration. Generally, a split-S2 includes the separate and distinct A2 and P2 components of S2. In certain examples, the at least one heart sound trend includes a split-S2 index during inspiration, a split-S2 index during expiration, the rate of change of a split-S2 interval during inspiration, the existence of a split-S2 during inspiration, etc.

Generally, during inspiration, negative intrathoracic pressure can cause increased blood return into the right side of the heart. The increased blood volume in the right ventricle can cause the pulmonic valve to stay open longer during ventricular systole. This typically can cause an increased delay in the P2 component of S2. Similarly, during expiration, the positive intrathoracic pressure can cause decreased blood return to the right side of the heart. The reduced volume in the right ventricle can allow the pulmonic valve to close earlier at the end of ventricular systole, typically causing P2 to occur earlier and closer in time to the A2 component of S2. The split-S2 sound can be heard generally in younger subjects and during inspiration. During expiration, the interval between the A2 and P2 components can shorten and the sounds can merge.

Typically, the A2 and P2 components of the split-S2 are wider and vary less with respiration during ventricular failure, atrial septal defects, pulmonary stenosis, etc., than during normal cardiac function. Thus, at 2150, the information about at least one cardiovascular status can include information about split-S2 variation during at least one phase of the respiration signal, such as inspiration or expiration.

In another example, the information about at least one cardiovascular status can include information about the difference between at least two heart sound trends, such as S1 amplitude during inspiration and S1 amplitude during expiration, or any other heart sound trend occurring during at least a first and a second at least a portion of at least one phase of the respiration signal.

FIG. 22 illustrates generally an example of portions of a method 2200 including automatically producing at least one heart sound trend, detecting information about a blood volume, and providing information about at least one cardiovascular status.

At 2225, at least one heart sound trend is automatically produced. The at least one heart sound trend can be automatically produced using at least one phase of a respiration signal and at least one heart sound. The at least one heart sound trend includes an index of information about at least one measurement, feature, characteristic, computation, or interval of at least a portion of at least one heart sound arranged, sorted, or otherwise indexed using at least a portion of at least one phase of the respiration signal. In an example, the at least one heart sound trend can be automatically produced using the processor 130.

At 2249, information about a blood volume is detected. The blood volume can include a stroke volume, cardiac output, etc. Typically, information about a blood volume can be determined, estimated, correlated, or otherwise detected using a respiration signal, such as a MV signal, a tidal volume signal, or other respiration signal, an impedance signal, such as a transthoracic impedance signal or other impedance signal, a pressure signal, such as a thoracic pressure signal or other pressure signal, a flow meter, etc. In an example, the information about a blood volume can be detected using the blood volume sensor 150.

At 2250, information about at least one cardiovascular status is provided. The information about the at least one cardiovascular status can be provided using information from the at least one heart sound trend and information about the blood volume. The information about at least one cardiovascular status can include information about heart failure, cardiac performance, ventricular performance, ventricular failure, atrial performance, ischemia, myocardial infarction, pulmonary stenosis, atrial septal defects, hypoperfusion, pulmonary congestion, etc. In an example, the information about at least one cardiovascular status is provided using an analysis module 145.

In an example, diagnostic information about ventricular performance can be determined by tracking heart sounds during different respiratory phases, such as inspiration or expiration. Generally, S1 provides information about the force of contraction of the heart. Further, blood volume is generally indicative of the preload of the heart, and typically varies with respiration. Therefore, using S1 and blood volume, the force of the contraction of the heart can be measured during different preloads. This measurement can provide valuable information about a cardiovascular status, such as ventricular performance.

In an example, the relationship between S1 (or any other measurement, feature, characteristic, computation, or interval of at least a portion of at least one heart sound signal or cardiac signal) and blood volume can be illustrated using a Frank-Starling curve. Generally, the Frank-Starling curve can be used to measure cardiac performance. The Frank-Starling curve typically demonstrates that performance of a failing heart can improve with either an increase in contractility or a decrease in afterload. An example of the Frank-Starling curve is shown in FIG. 13.

In an example, the operating slope of the Frank-Starling curve can be measured as the rate of change of at least one measurement, feature, characteristic, computation, or interval of at least a portion of at least one heart sound over the rate of change of blood volume 1302 (“ΔV”). In an example, the operating slope of the Frank-Starling curve can be measured as the ΔS1 over ΔV.

In another example, the operating slope of the Frank-Starling curve can be measured as the rate of change of at least one measurement, feature, characteristic, computation, or interval of at least a portion of at least one heart sound occurring during at least a portion of at least one phase of a respiration signal over ΔV, such as S1 during inspiration over ΔV, S1 during expiration over ΔV, etc. Generally, trending S1, or any other heart sound or heart sound timing, separately during inspiration, expiration, or any other at least one phase or portion of at least one phase of the respiration signal can be used with ΔV to measure the slope of the Frank-Starling curve. Thus, at 2250, the information about at least one cardiovascular status can include information about the slope of the Frank-Starling curve during inspiration and expiration, inspiration, expiration, or at least a portion of at least one phase of the respiration signal.

In another example, at 2250, the information about at least one cardiovascular status can include information about one or more than one slope of the Frank-Starling curve during at least a portion of at least one phase of the respiration signal, or a comparison between at least a first slope of the Frank-Starling curve during a first phase of the respiration signal and a second slope of the Frank-Starling curve during a second phase of the respiration signal.

In certain examples, some or all of the functionality of one or more than one component, such as the respiration phase detector 115, the heart sound detector 125, the gating circuit 126, or the analysis module 145, can be included in the implantable or external processor 130.

In the examples of FIG. 1-22, various examples, including sensing a respiration signal, detecting at least one phase of a respiration signal, sensing a heart sound signal, detecting at least one heart sound signal, automatically producing at least one heart sound trend, sensing a cardiac signal, gating the heart sound signal, enabling or disabling the heart sound sensor, displaying the at least one heart sound trend, providing information about at least one cardiovascular status, or detecting information about a blood volume, are disclosed. It is to be understood that these examples are not exclusive, and can be implemented either alone or in combination, or in various permutations or combinations.

It is to be understood that the above description is intended to be illustrative, and not restrictive. For example, the above-described embodiments (and/or aspects thereof) may be used in combination with each other. Many other embodiments will be apparent to those of skill in the art upon reviewing the above description. The scope of the invention should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. In the appended claims, the terms “including” and “in which” are used as the plain-English equivalents of the respective terms “comprising” and “wherein.” Also, in the following claims, the terms “including” and “comprising” are open-ended, that is, a system, device, article, or process that includes elements in addition to those listed after such a term in a claim are still deemed to fall within the scope of that claim. Moreover, in the following claims, the terms “first,” “second,” and “third,” etc. are used merely as labels, and are not intended to impose numerical requirements on their objects.

The Abstract is provided to comply with 37 C.F.R. § 1.72(b), which requires that it allow the reader to quickly ascertain the nature of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. Also, in the above Detailed Description, various features may be grouped together to streamline the disclosure. This should not be interpreted as intending that an unclaimed disclosed feature is essential to any claim. Rather, inventive subject matter may lie in less than all features of a particular disclosed embodiment. Thus, the following claims are hereby incorporated into the Detailed Description, with each claim standing on its own as a separate embodiment. 

1. A system comprising: an implantable medical device, including: a respiration sensor, configured to sense a respiration signal; and a heart sound sensor, configured to sense a heart sound signal; an implantable or external respiration phase detector, coupled to the respiration sensor, configured to detect at least one phase of the respiration signal; an implantable or external heart sound detector, coupled to the heart sound sensor, configured to detect at least one heart sound of the heart sound signal; and an implantable or external processor, coupled to the respiration phase detector and the heart sound detector, wherein the processor is configured to automatically produce at least one heart sound trend over at least a portion of at least one respiration cycle using the at least one heart sound, the at least one heart sound trend occurring during a specified at least a portion of at least one phase of the respiration signal.
 2. The system of claim 1, wherein the at least one heart sound trend includes at least one measurement, feature, characteristic, computation, or interval of at least one heart sound.
 3. The system of claim 2, wherein the at least one measurement, feature, characteristic, computation, or interval of at least one heart sound includes at least one of an amplitude of a heart sound, a time interval between a first heart sound and a second heart sound, an energy of a heart sound, and a normalized measurement, feature, characteristic, computation, or interval of the heart sound signal by another measurement, feature, characteristic, computation, or interval of the heart sound signal.
 4. The system of claim 1, wherein the implantable medical device includes: a cardiac sensor, coupled to the heart sound detector, configured to sense a cardiac signal; and wherein the heart sound detector is configured to detect at least one heart sound of the heart sound signal using information from the cardiac signal.
 5. The system of claim 4, wherein the at least one heart sound includes at least one measurement, feature, characteristic, computation, or interval between at least one cardiac signal feature and at least one heart sound feature.
 6. The system of claim 4, including an implantable or external gating circuit, coupled to the cardiac sensor and the heart sound detector, wherein the gating circuit is configured to obtain a gated heart sound signal by gating the heart sound signal using information from the cardiac signal, and wherein the heart sound detector is configured to detect at least one heart sound of the gated heart sound signal.
 7. The system of claim 4, wherein the heart sound sensor is coupled to the cardiac sensor, wherein the heart sound sensor is enabled or disabled using information from the cardiac signal.
 8. The system of claim 1, wherein the heart sound sensor is coupled to the respiration sensor, wherein the heart sound sensor is enabled or disabled using information from the respiration signal.
 9. The system of claim 1, wherein the heart sound sensor is coupled to the respiration phase detector, wherein the heart sound sensor is enabled during the specified at least a portion of at least one phase of the respiration signal.
 10. The system of claim 1, including an implantable or external gating circuit, coupled to the respiration phase detector and the heart sound detector, wherein the gating circuit is configured to obtain a gated heart sound signal by gating the heart sound signal using information from the respiration phase detector, and wherein the heart sound detector is configured to detect at least one heart sound of the gated heart sound signal.
 11. The system of claim 1, including an external display, coupled to the processor, wherein the display is configured to display information from the processor.
 12. The system of claim 1, including an implantable or external analysis module, coupled to the processor, wherein the analysis module is configured to provide information about at least one cardiovascular status using information from the at least one heart sound trend.
 13. The system of claim 12, wherein the analysis module is configured to provide information about the at least one cardiovascular status using information from the at least one heart sound trend occurring during at least a portion of the at least one specified phase of the respiration signal.
 14. The system of claim 12, wherein the implantable medical device includes an implantable blood volume sensor, coupled to the processor, wherein the blood volume sensor is configured to detect information about a blood volume.
 15. The system of claim 14, wherein the analysis module is configured to provide information about the at least one cardiovascular status using information from the at least one heart sound trend and the blood volume sensor.
 16. The system of claim 15, wherein the analysis module is configured to provide information about the at least one cardiovascular status using information from the at least one heart sound trend occurring during at least a portion of at least one specified phase of the respiration signal and using information from the blood volume sensor.
 17. A system comprising: means for sensing a respiration signal within a body; means for detecting at least one phase of the respiration signal; means for sensing a heart sound signal within the body; means for detecting at least one heart sound of the heart sound signal; and means for automatically producing at least one heart sound trend, over at least a portion of at least one respiration cycle, wherein the at least one heart sound trend is indicative of at least one heart sound occurring during a specified at least a portion of at least one phase of the respiration signal.
 18. A method comprising: sensing a respiration signal using an implanted respiration sensor; detecting at least one phase of the respiration signal; sensing a heart sound signal using an implanted heart sound sensor; detecting at least one heart sound of the heart sound signal; and automatically producing at least one heart sound trend, over at least a portion of at least one respiration cycle, wherein the at least one heart sound trend is indicative of at least one heart sound occurring during a specified at least a portion of at least one phase of the respiration signal.
 19. The method of claim 18, wherein automatically producing the at least one heart sound trend includes automatically producing at least one measurement, feature, characteristic, computation, or interval of at least one heart sound.
 20. The method of claim 19, wherein automatically producing at least one measurement, feature, characteristic, computation, or interval of at least one heart sound includes at least one of an automatically producing an amplitude of a heart sound, automatically producing a time interval between a first heart sound and a second heart sound, automatically producing an energy of a heart sound, and automatically producing a normalized measurement, feature, characteristic, computation, or interval of the heart sound signal by another measurement, feature, characteristic, computation, or interval of the heart sound signal.
 21. The method of claim 18, including: sensing a cardiac signal using an implanted cardiac sensor; and wherein the detecting at least one heart sound includes using information from the cardiac signal.
 22. The method of claim 21, wherein the automatically producing at least one heart sound trend includes automatically producing at least one measurement, feature, characteristic, computation, or interval between at least one cardiac signal feature and at least one heart sound feature.
 23. The method of claim 21, including gating the heart sound signal using a gating circuit to detect at least one heart sound, wherein the gating the heart sound signal includes using information from the cardiac signal.
 24. The method of claim 21, including enabling or disabling the heart sound sensor using information from the cardiac signal.
 25. The method of claim 18, including enabling or disabling the heart sound sensor using information from the respiration signal.
 26. The method of claim 18, including enabling the heart sound sensor during at least one of the specified at least a portion of at least one phase of the respiration signal.
 27. The method of claim 18, including gating the heart sound signal to detect at least one heart sound, wherein the gating the heart sound signal includes gating the heart sound signal using information from the respiration signal.
 28. The method of claim 18, including displaying the at least one heart sound trend.
 29. The method of claim 18, including providing information about at least one cardiovascular status using information from the at least one heart sound trend.
 30. The method of claim 29, wherein providing information about at least one cardiovascular status includes using information from the at least one heart sound trend occurring during specified different first and second phases of the respiration signal.
 31. The method of claim 29, including detecting information about a blood volume using an implanted blood volume sensor.
 32. The method of claim 31, wherein providing information about the at least one cardiovascular status includes using information from the at least one heart sound trend and using information about the blood volume.
 33. The method of claim 32, wherein providing information about the at least one cardiovascular status includes using information from the at least one heart sound trend occurring during specified different first and second phases of the respiration signal and using information about the blood volume. 